Weird Aircon problem, CLK320

PhilTilson

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I have a problem with my CLK320 aircon in that, for about five weeks now, I have been getting no air from the vents/outlets. It doesn't matter whether the A/C is on or off, or whether it's on Manual or Auto. The fan runs fine, but there is virtually no air exiting - UNLESS the Recirc button is pressed. I then get air from all vents as normal!

Now, I know this doesn't make sense. I know that all the Recirc button does is move a flap to take air from inside rather than outside... But this is what happens! You can hear it very clearly, too. Without Recirc, the fan is running, but quietly; press Recirc and you can hear the air coming from the vents though the fan speed doesn't change.

My local Benz experts have had a look but can't explain it. It doesn't help that, on rare occasions, everything seems to work OK for a few minutes and, of course, these always coincide with the time I take it to the repair shop! This is why I have discounted a blocked filter (for the moment, at least!)

But I am not imagining this. I have undertaken several long journeys recently and suffered very cold feet due to lack of heating. From time to time I press the Recirc button and get some warm air into the car, but you can't run all day on recirculating air.

Does anyone have any idea what may be causing this? The diagnostics show nothing wrong, apparently. I am baffled.
 

whitenemesis

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As you get air when in RECIRC mode, check the cabin air filter, probably blocked and/or soaking wet.
 

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If you get enough warm air to the feet then not a filter fault, your car Sir, is it a 208 or 209 as 2 very different systems
 
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PhilTilson

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It's a 209, 2006. And at this moment, it's all working perfectly - because I have just come back from the repair shop attempting to demonstrate how it doesn't work! This is why I don't think it can be a filter problem.

Is it possible that the flap/motor that controls the fresh/recirc side could be blocked/jammed/damaged and yet still not show up on the whizzy computer that the repair guys connect it up to?
 

whitenemesis

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Do you have Thermatic (analogue) or Thermatronic (digital) system?

The system will distribute air as normal in whichever mode it's in, RECIRC or normal. The only difference is in normal mode it is drawing air through the cabin filter in the engine compartment.

Your local "Benz" experts, do they use STAR to read the error codes? 'Cos there will be codes stored in the climate control module if any part of the system fails (except if there is a blocked filter)
 
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PhilTilson

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Yes, they use the STAR system and say there are no error codes showing.

I'm not sure whether the system is Thermatic or Thermatronic. I suspect the former as the controls are analogue and there is no digital display.

I take what you say about the Recirc vs Normal modes. My thinking was this: say there was some obstruction (like a blocked filter, but unlikely as it works sometimes) on the fresh air inlet. Then I would get air on recirc, as the cabin inlet would not be blocked, but no air on 'fresh' as the air intake wouldn't allow any in. That's the only rational explanation I can think of for these symptoms.

But given that it works on occasions, I can't see it can be a blocked filter, which is why I'm wondering if there's some flap or other that is intermittent. But then, why doesn't it show up on STAR?

Now you see why I say it's weird!!
 

whitenemesis

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Have you actually checked the filter, just for completeness?
 

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This is the same system as the 203, all motors and flaps, in the DIY section there is an article on how to reset the flaps on a 203, please try it.

The air filter cannot cause a system to be fine one day and not the next.
 
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PhilTilson

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Haven't checked the filter as I'm thinking along the same lines as Malcolm!

Went out again a couple of hours ago and all working perfectly. But I can guarantee that the next time I have a long journey in cold conditions, it won't work! Not because of the cold, but because of Murphy's Law.

I'm going to get the guys to check all around the flap that controls the inlet air. I am sure it must have something to do with that.

Unless anyone knows better!
 
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PhilTilson

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Problem solved - I think! And it may be worth explaining as it may happen to others.

Logic said that if I got air on Recirc, but not otherwise, then the fresh air inlet must be obstructed. But this didn't explain why it worked sometimes, especially as no fault was flagged on STAR.

First job was to check the operation of the fresh air flap - this worked perfectly. But a look at the pollen filter showed it to be seriously clogged. Now, you may say that this should have been the first port of call, but it seemed this could not be the problem because sometimes it worked!

The solution, I believe, is in the fact that the filter cartridge has plastic fins or flaps around the edge to help seal it. On the removed filter, there was quite a gap at both ends. My guess is that sometimes, the air was able to pass through these gaps and the system therefore seemed to be working normally, even though it was probably below par.

On other occasions, perhaps due to temperature, humidity or whatever, the airflow was sufficient to suck the fins outwards and seal the gaps, rather like a vacuum cleaner, and in this case, no air could get through.

Switch to Recirc and, of course, everything was fine - as was the normalising procedure, since all flaps etc were working as they should.

Only time will tell, but I'm feeling fairly confident. Moral of the story - look for the obvious!
 

hsloco

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Only time will tell, but I'm feeling fairly confident. Moral of the story - look for the obvious![/QUOTE]

Which is what WN was saying all along!
 

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